Off-road vehicles, such as heavy equipment used in construction, forestry, mining, and other industries, are often used in low ambient temperature environments and in remote locations and may be exposed to multiple types of fire hazards. A vehicle fire that is not effectively suppressed could threaten the safety of the operator and destroy the equipment. Therefore, it is customary practice to crimp off-wad heavy equipment vehicles with on board fire extinguishing and suppression systems. In addition to performing effectively under harsh conditions and low temperatures, any fire fighting agent to be used in a fire extinguishing and suppression system on such vehicles must be able to suppress both class A and class B fires.
Conventional on-board fire suppression systems for use in connection with off-road heavy equipment vehicles exposed to low temperature environments discharge a dry chemical fire extinguishing agent, such as for example monoammonium phosphate, to initially suppress fire. While performing extremely well in knocking down a fire, dry chemical fire extinguishing agents provide minimal protection against possible reflash. Thus, a secondary discharge of wet chemical agent sometimes follows the discharge of the dry chemical agent for cooling hot surfaces in order to prevent relish and for coating surfaces thereby securing those surfaces. Conventional wet chemical agents include an aqueous solution of a single salt or an aqueous foaming solution. Because of the low ambient temperatures to which an off-road vehicle may be exposed, wet chemical agents, whether used for extinguishing the fire per se or used for cooling purposes in combination with a dry chemical fire extinguishing agent in such off-road vehicle fire suppression systems, include a freezing, point depressant, for example, a glycol, such as ethylene or propylene glycol, or a single salt solution, such as an aqueous, solution of potassium acetate or potassium lactate, or a combination of a single salt and either ethylene or propylene glycol.
U.S. Pat. No. 5,651,416 disc loses a meth for extinguishing a fire in an engine compartment or crew compartment using a water based solution including an acetate, chloride, bromide or iodide salt of an alkali metal or ammonium ion, a freezing point, depressant, and a surfactant. Potassium acetate is disclosed as acting as both a tire extinguishing agent and a freezing point depressant. It is stated in U.S. Pat. No. 5,651,416 that at a concentration of 9.0 to 9.5 grams of potassium acetate for every 10 milliliters of water combined with 1 gram of soap, the potassium acetate will be saturated in water at a temperature of −60° F. to −65° F. (−51.1° C. to −53.9° C.).
U.S. Pat. No. 6,231,778 discloses an aqueous foaming fire extinguishing composition suitable for use and storage at a temperature below −1° C. comprising an aqueous solution of 50-60% by weight of 60% aqueous solution of potassium acetate, 7-10% by weight of a 3% solution of aqueous film-forming foam, and 15-20% by weight alkylene glycol selected from the group consisting of ethylene glycol and propylene glycol, and the balance being water.
Whether the salt solution is used as a fire extinguishing agent per se or in combination with dry chemical fire extinguishing agent as a chemical cooling agent, the high salt concentration required to prevent freezing of the aqueous solution in subfreezing ambient temperature environments can reduce the overall environmental acceptability of the fire suppression system. Additionally, the fire fighting effectiveness may be adversely affected since the viscosity of the wet fire extinguishing agent increases as the salt concentration increases and as the temperature decreases. The increased viscosity at low temperatures makes it difficult to obtain a spray at the nozzle. Instead of spraying from the nozzle, these agents at extreme low temperatures may discharge gas a stream which severely limits the coverage area. Another disadvantage lies in the environmental implications of the type of freeze point depressants used. Both propylene and ethylene glycol are toxic substances and must, when used as the sole freeze point depressant, be used in large quantities to obtain the required freezing point. Additionally, an aqueous solution containing a high concentration of glycols may itself be flammable. With pressure to develop more environmentally friendly products, it is desirable to avoid these types of freeze point depressants altogether.